The present invention relates to an audio current pick-up device and, particularly, to such a device for picking-up audio information from an electric current flowing through an electric wire.
In order to pick-up audio information from a minute electric current flowing through an electric wire such as a telephone cord, it is usual to use a receiver including an amplifier having a high amplification factor. Since, in such a scheme, there is a tendency to generate howling in the receiver, it is difficult to increase the sound output to a level high enough to be heard. This is particularly true when the receiver is a hearing-aid.
As to a conventional receiver for picking-up an audio information from a minute electric current flowing an electric wire, FIG. 7 shows a hearing-aid 2 in intimate contact with a telephone receiver 1. The hearing-aid 2 includes an induction coil therein which picks up magnetic flux leakage from the receiver 1 and provides an electric signal corresponding to a variation thereof. The signal is amplified by an amplifier of the hearing-aid 2 having an amplification function and a frequency characteristics correction function to a level suitable for the user so that he can hear it through an earphone (not shown) connected to a cord 3.
A further conventional scheme is shown in FIG. 8 in which a telephone coil 4 is mounted on a receiver 1. Magnetic flux leakage from the receiver is picked up by the coil 4 an electric output signal of which is supplied through a wire 5 to a user's hearing-aid 2.
In the scheme shown in FIG. 7 or 8, it is impossible to pick up a sound current of practically sufficient S/N ratio when the magnetic flux leakage from the telephone receiver 1 is small.